Typical photographic elements use silver halide emulsions, the silver halide having a native sensitivity to ultraviolet radiation. Ultraviolet radiation ("UV") as used in this application means light having a wavelength of 300-400 nm. Such UV sensitivity is usually undesirable in that it produces an image on the photographic element which is not visible to the human eye. Furthermore, the image dyes in the color photographs are known to fade due to action of UV light. Also other organic molecules such as unused color forming couplers in the emulsion layers and optical brightners in the paper support degrade due to action of UV light and generate undesirable color stains on the finished photographs. Therefore, photographic elements typically contain a UV absorbing compound (sometimes referred to simply as a "UV absorber"). Another function of UV absorbers is to prevent the formation of undesirable patterns caused by electrostatic discharge in silver halide photographic materials. In general, UV absorbers impart light stability to organic molecules in various products which are susceptible to degrade as a result of the action of UV.
Generally, an effective UV absorber should have its peak absorption above a wavelength of 320 nm. The absorption peak may be at a longer wavelength, as long as absorption drops off sufficiently as it approaches the visual range (approximately 400 to 700 nm) so that no visible color is shown by the compound. In addition, to be effective, a UV absorber should have a high extinction coefficient in the desired wavelength range. However, for the most desirable UV protection, the high extinction coefficient should be at those wavelengths sufficiently below the visual range so that the compound should not be visually yellow.
Both conventional and polymeric UV absorbers have been used in photographic elements. Examples of conventional (that is, non-polymeric) UV absorbing compounds are shown by formula (IIA) and (IIB) below, currently used in color paper as a mixture have the following structures. ##STR2##
It has however, been observed that these compounds and other non-polymeric UV absorbers have a propensity to crystallize out in the coatings. This results in migration of the compound to the surface causing an undesirable blooming effect. Recently, it has been suggested that such compounds are associated with high health risk factors.
The benzotriazole class of polymers having monomeric units from formula (III) below, their synthesis, and use in various plastic formulations, are described in U.S. Pat. No. 3,072,585. ##STR3## EP-A-0 190 003 B1 describes photographic elements containing polymers of formula (III). Photographic elements containing other polymers of formula (IV) below are disclosed in allowed U.S. patent application Ser. No. 07/907,008 by Chen et al. filed Jul. 1, 1992. ##STR4##
Polymers of formula (III) and (IV) are highly useful in photographic elements. However, they tend to have a hypsochromically shifted (that is, shifted to shorter wavelengths) absorbance position in silver halide photographic elements, with respect to current photographic element dispersions of conventional UV absorbers of formula (IIA) and (IIB). Although this hypsochromic shift allows optical brightners on a paper support to act more efficiently for an increased whiteness, it allows sufficient UV light to reach image dyes and optical brightening molecules causing their photolytic degradation. Many magenta image dyes are also more prone to such degradation with a hypsochromically shifted UV absorber.
An additional problem with the monomer (III) has been the cost associated with its synthesis. The monomer (III) is generated by alkylating its precursor (V) with moderately expensive vinyl benzyl chloride. In addition to its expense, the yield of the monomer (III) is lowered due to formation of the dialkylated by-product (VI) even under carefully controlled monoalkylation procedures reported in the literature. ##STR5##
U.S. Pat. No. 3,213,058 though, does mention the conversion of (V) to (VII) using base-catalyzed alkylation with chloroethanol or bromoethanol or ethylene oxide under higher temperature/pressure condition. ##STR6##
The use of ethylene carbonate (VIII): ##STR7## to attach a hydroxyethyl substituent has been known in various chemical reactions. In particular, it was described for use with benzophenones in U.S. Pat. No. 4,885,396; in the hydroxyethylation of thiophenol, Y. Tamura, et al, Synthesis, 641 (1975); in the hydroxyethylation of thiophenol using 18-Crown-6 as a catalyst, M. Lissel, S. Schmidt and B. Neumann, Synthesis-Stuttgart (5), 382-383 (1986); and in the hydroxyethylation of perfluroalkanol S. M. Heilman L. R. Krepski, D. M. Moren, and J. K. Rasmussen, U.S. Pat. No. 4,906,792.
It is desirable then to have additional classes of UV absorbers from which one can select for various applications, particularly for photographic uses. It is additionally desirable, although not necessary, to design new UV monomeric absorbers which would have an absorbance position close to or slightly better than the currently used combination of UV compounds (IIA) and (IIB) while maintaining the effect from optical brightening compounds. It is additionally desirable that the compound can be readily made in good yields with low levels of unwanted products.